Periodontal disease provides an opportunity to understand the processes that lead from immune homeostasis to chronic inflammation. The ability to eliminate a selected microbe from a biofilm consortium would provide an essential tool for determining the role of putative pathogens in the progression of events that lead to chronic inflammation and the potential of commensals to mitigate this destructive immune response. More broadly, commensal microbial communities play an integral role in maintaining the health of a number of mucosal systems and selective killing agents will be needed for effective treatment of mucosal infections at these non- sterile interfaces. We successfully targeted biofilms of the periodontal pathogen Aggregatibacter actinomycetemcomitans (Aa) with a photosensitizer and obtained light activated killing. We used a monoclonal antibody (mAb) as the targeting moiety. Transport of biomolecules the size of mAb into biofilms is significantly hindered. There are currently no small molecular weight targeted killing agents for Aa, and there are no general methods for producing small molecular weight selective targeting moieties against any given bacterial pathogen. Our objective is to fill both these gaps. Small molecular weight agents will not only have the advantage of rapid transport into periodontal pockets and Aa biofilm, but are less likely to be antigenic and will be more appropriate for routine synthesis and application. We will pursue two approaches for producing targeted killing agents against Aa: 1) Phage display (Specific aim 1). We will use established protocols for screening peptides with high affinity for three targets: Aa biofilm, Aa LPS and an Aa outer membrane protein. We will construct homo and hetero dimer pairs of high affinity peptides conjugated to a photosensitizer (PS). 2) Antibody CDR dimers (Specific aim 2). Using a collection of anti-Aa mAb as a starting point we will produce small molecular weight targeting peptides consisting of complementarity determining regions (CDRs). CDRs exhibiting high affinity to Aa biofilm will be coupled via a hydrophilic spacer and conjugated to a PS. Successful completion of our specific aims will produce a tool that can be used to probe the role of Aa in periodontal disease progression in both animal and human studies and provide an approach for producing small molecular weight targeted killing agents against a variety of periopathogens.